Rechner cuts time out of your addition and subtraction by using swipe gestures to make calculations, rather than on screen buttons.

While the interface may take a bit of getting used to, the gestures are definitely nicer and faster than pressing a button—and it makes the other buttons bigger so they're easier to tap, too. It only has gestures for addition, subtraction, equals, and clear—not multiplication and division, strangely—but you can access a number of other functions by swiping down. The developers claim its "200% more efficient" than a traditional calculator—though that's probably only true if your main operations are addition and subtraction. When you add other things into the mix, swiping down to access those buttons can make the whole thing more inefficient pretty quickly. We'd really like to see gestures for multiplication and division—like diagonal swipes (why isn't this in there already?)—but for now, it's a pretty cool alternative to iOS' default calculator app. Check out the video above to see it in action.